Method and apparatus for controlling reduction furnaces



J. R. GREEN ET AL Feb. 19, 194s.

METHOD AND APPARATUS FOR CONTROLLING REDUCTIGN FURNACES Filed Nov, l5, 1945 4 Sheets-Sheet 1 Illffffmw IN1/Emol; JOHN n. GREEN JOSEPH P. VQLLRATH Feb. 19, 1946. J. R. GREEN ET Ax. 2,395,335

METHOD AND APPARATUS FOR coNTnoLLrNG REDucTIoN FURNAcEs Filed Nov. 1:5, 1945 4 sheets-Sheet 2 INVENTOR. JOHN R. GREEN P. BY JOSEPH VOLLRATH ATTOR EY.

Feb. 19, 1946.V J, R- BEEN ET AL 2,395,385

METHOD AND APPARATUS FOR CONTROLLING REDUCTION FURNACES Filed Nov. 13, 1943 4 Sheets-Sheet 3 FIG. 3

INVENTOR. JOHN R. GREEN JOSEPH P VOLLRATH i ATTONEY.

Feb. 19, 1946. J, r.;- GREEN ETAL 2,395,385

METHOD AND APPARATUS Foa CONTRQLLING REDUCTION runucs Filed Nov. 13, 1945 sheets-sheet 4 IIS INVENTOR. JQHN R GREEN JOSEPH P VOLLRATH ATToR EY.

Patented Feb. 19, 1946 METHOD AND APPARATUS FOB CON- TROLLING REDUCTION FURNACES John It. Green. Mount Lebanon, and Joseph P. Vollratli, Glemide, Pa., assignors to The Brown Instrument Company. Philadelphia, Pa., a corporation of Pennsylvania Application November 13, 1943, Serial No. 510,124

(ci. vs -4i) 8Clalms.

The general object of the present invention is to provide an improved method of and improved apparatus for controlling the operation of an ore reduction furnace. More specincally the object of the invention is to provide a method of and means for controlling the operation of an ore reduction furnace by and in response to variations in the value of a property or condition of the gas leaving the furnace which can readily be measured continuously and which provides a reliable indication of the reducing capacity of the furnace atmosphere, and of the corrective steps which should be taken when that capacity is impaired. The invention is of especial utility in controlling the operation oi" iron ore reducing furnaces making use of both hydrogen and carbon monoxide as significant reducing agents.

One characteristic or property of the exit gas well adapted for measurement for control purposes in accordance with the present invention, is the thermal conductivity of the gas. Qrdinarily in reducing iron ore under steady operating conditions in any particular furnace the thermal conductivity of the furnace exit gas will have a particular or optimum value when the operating eiiiciency is at a practical maximum. Ordinarily, under such steady operating conditions, an increase or decrease in the thermal conductivity of the furnace exit gas will indicate a decrease in the eiliciency of the furnace resulting from a change in the reduction capacity of the furnace atmosphere and which can be corrected by furnace adjustments dependent on the direction of departure oi the thermal conductivity from its optimum value and tending to restore that value.

Control of a reduction furnace of the general type specined yin response to the thermal conductivity of the exit gas is practically effective, we believe, because in the regular operation of such a furnace the thermal conductivity of the exit gas changes significantly only as a result of changes in the hydrogen and carbon 'dioxide constituents of the gas. Other exit gas constituents which may significantly effect the exit ses thermal conductivity. such as nitrogen, carbon monoxide and oxygen all have about the same thermal conductivity as air, whereas the thermal conductivity of hydrogen is much higher, and the thermal conductivity of carbon dioxide is substantially lower than that of air. more, while carbon dioxide is not a reduciusr agent, it varies in substantial inverse accordance with the carbon monoxide content of the furnace exit gas under usual operating conditions, since in the` regular operation of any par ticular furnace, the carbon oxide` content (C0002) of the exit gas will be approximately constant.

In regulation in accordance with the present invention, on an increase in the thermal conductivity of the exit gas above its optimum value, corrective furnace adjustments are made to lower the reducing capacity of the furnace atmosphere by reducing its hydrogen content, and/or increasing its CO2 content and thereby decreasing the CO content. Conversely, when the thermal conductivity decreases below its optimum value, corrective adjustments are made to increase the hydrogen content and/or to decrease the C0: content of the furnace gas.

'I'he thermal conductivity of the exit s as is not the only gas property or characteristic suitable for measurement for control purposes in accordance with the present invention. For example, under steady operating conditions, the density of the exit gas from any particular reduction furnace has an optimum value when the furnace efficiency is at a practical maximum and variations in the exit gas density require corrective furnace adjustments analogous to those required when the thermal conductivity of the exit gas falls below and rises above the optimum thermal conductivity. The gas density provides a reliable indication of the reducing capacity of the furnace atmosphere because the molecular weights of carbon monoxide and nitrogen do not diii'er markedly from one another or from the average molecular weight of the gaseous constituents of air, whereas the molecular weight of carbon dioxide is substantially higher and the molecular weight of hydrogen is much smaller than said average molecular weight.

In consequence, a variation in the density of the furnace exit sas indicates a variation in the reducing capacity of the furnace atmosphere. On a decrease in the density of exit gas below the optimum density value, furnace operations will be improved by decreasing the hydrogen content and by increasing the carbon dioxide content of the furnace gases, Conversely, when the density of the exit gas rises above the optimum density value. the proper corrective adiustments will increase the hydrogen content and decrease the C01 content oi the gas.

The llame structure of a burning iet of gas varies with the composition of the gas, and when the burning consists wholly or in substantial part of the gas leaving a reducing furnace flame structure provides a measurable indication of the reducing character of the furnace atmosphere which may be used in regulating the operation oi' the furnace in accordance with the present invention.

The present invention is well adapted for use in controlling iron ore reduction furnaces of various types. In particular it is well adapted for use in controlling the operation of blast furnaces having special provisions. hereinafter described, for passing hydrogen into the furnace at a level well above the furnace fusion line. The invention is also well adapted for use in controlling so-called direct reduction furnaces in which hydrogen is employed as the sole or main reducing agent, and is especially well adapted for use in controlling the operation of a direct re'ductlon furnace in which carbon as well as hydrogen is supplied to the furnace chamber.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, the advantages and specnc objects obtained with its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described preferred embodiments of our invention.

Of the drawings:

Fig. 1 is a diagrammatic view illustrating the use of the present invention in controlling the operation of a blast furnace;

Fig. 2 is a diagram of electrical measuring and control portions of the apparatus shown in Fig. l;

Fig. 3 is a diagram illustrating a proportioning control system included in the apparatus shown in Fig. 2;

Fig. 4 is a diagrammatic view illustrating the use oi' the invention in controlling the operation of a direct reduction furnace;

Fig. 5 is a diagrammatic view illustrating a modification of apparatus shown in Fig. 2; and

Fig. 6 is a diagrammatic view illustrating another modification of apparatus shown in Fig. 2.

In Fig. 1 we have illustrated the use of our invention in controlling the operation of a blast furnace l'ii which is of conventional type and form except for its inclusion of special means for passing hydrogen gas into the stack as hereinafter described. The blast furnace is provided with the usual charging or feeding means li at its upper end and is provided at its lower end with a hearth having a cinder notch I2, and molten metal tap hole i3, and with water cooled boch plates Il and tuyres il. Cooling water is supplied to and exhausted from the water cooled tuyres and bo'sh plates by piping I1 and i8. The tuyres are supplied with .preheated air or "hot blast through a bustle pipe or manifold Il. Special inlets i9 through which hydrogen is passed into the furnace are shown as arranged substantially midway between the upper and lower ends of the blast furnace masonrystack and are supplied with hydrogen through a bustle pipe 2l. In ordinary practice the hydrogen thus supplied to the furnace will bevthe hydrogen constituent of some available gaseous mixture, ordinarily coke oven gas, which is rich in hydrogen. I'he hydrogen content of ordinary coke oven gas is between 55 and 80% by volume. The gas discharged from the furnace passes from the upper end of the blast furnace through a pipe 2| into prising a dust remover 22 and usually comprising other conditioning devices to which the gas passes from the dust remover 22 through the pipe 22. Such other conditioning devices are not shown in Fig. l, but ordinarily comprise gas cooling and cleaning apparatus including a gas washer in which, as is explained in connection with Fig. 4, much of the water vapor in the gas is condensed and some of the carbon dioxide is washed out of the gas.

In respect to all of its features above mentioned. other than the hydrogen inlets I9 and pipe 20. the blast furnace shown in Fig. l is of the conventional type and form. Furthermore, said blast furnace is capable of operation in the most usual manner when the supply of hydrogen lo the inlets I8 is interrupted. The hot blast air supplied to the tuyres I5 is passed into the bustle pipe i6 under suitable pressure by a blower or blowing engine 24 through a humidity regulating unit or device 25, a volume regulator 28. one or more hot stoves 21 and `a bypass 21' about said stoves, and a hot blast temperature regulator 28. The latter is, in effect, a bypass control valve which is adjusted by a reversible control motor 3l to vary the relative portions of the blast air passing respectively through the hot stoves 21 and through the bypass pipe 21', and thus regulates the temperature of the mixture of heated and non-heated air passing to the bustle pipe i6 from the regulator 28.

The humidity regulator 2l may be adjusted by a reversible control motor 29 to increase or decrease the moisture content of the blast air. Usually, the general effect of the device 25 is to reduce the moisture content of the blast air more or less, 4but in blast furnace operation with a so-called "wet blast the humidity regulator 2i may usually operate to increase rather than to decrease the blast moisture content. The volume regulator 26 is adjusted by a reversible control motor 30 as required to maintain the desired weight rate of blast air flow into the furnace. Iron ore, coke and limestone or other uxins agent are supplied to the blast furnace tops or feeder Il by a skip car 32, approximately at rates indicated to the operator as appropriate by an indicator 32' adjusted by a reversible motor Il. The rate at which coke oven gas or other hydrogen containing gas is supplied to the bustle pipe 2li is regulated by adjustment of a regulator 84 effected by a reversible motor ll.

As shown in Fig. l, a small sample stream of gas passes continuously from the main 2l through gas treating means Il and a pipe 21' to measuring apparatus l1. The sample conditioning apparatus Il may well be or include an electrostatic preeipitstor. and as diagrcmmatically shown in Fig. 2 the measuring apparatus 31 comprises thermal conductivity test gas and standard gas cells "o and 31h. respectively, connected in an eiserne vtriage cimas having output terminals 21e and 31d. The measuring apparatus 31 operstes to create between the bridge output terminale a minute voltage which varies in accordance with the thermal conductivity of the gas passim through the test cells 21o. This voltage is measured by a suitable voltage measuring device l! and the latter operates through control apparatus I! comprising a control panel and associated relay mechanism to operate each of the above mentioned reversible control motors 2l. III. 3l.

y 32 and ll in a direction and to the extent dependot the thermal conductivity oi' the test gas from a predetermined` value thereof.

As shown diagrammatically in Fig. 2, the measuring device 3B is a self-balancing recording potentiometer instrument including a slide wire resistor 4I energized by a battery 4l'. One end of the resistor 40 is connected to the bridge output terminal 31e, and the second bridge output terminal 31d is connected through the input circuit of an electronic amplier 4| to a slider or adjustable contact 42 in sliding engagement with the resistor 40. As diagrammatically indicated in Fig. 2. the contact 42 is attached to and .supported by the pen carriage 43 which is adjusted longitudinally of the resistor 40, and thereby adjusts the index and recording elements o! the instrument 38. as well as the contact 42. when current flows in the output circuit of the bridge.

In the normal or balanced condition of the measuring apparatus, no current flows through the comparison cell bridge output circuit because the potential diilerence between the terminals )1c and 31d is then equal and opposite to the potential i drop in the portion of the slide wire resistor 40 between the point at which it is engaged by the contact 42 and the point at which it is connected to the terminal conductor llc. An increase or decrease in the potential difference between the bridge output terminals 31o and 31d unbaiances the measuring apparatus and produces a corresponding current flow through the input circuit of the ampliiler 4 I. The latter is therebyV actuated to energize a reversible motor 44 for rotation in the direction and to the extent needed to rebalance the measuring apparatus.

That rebalancing operation is effected by the adjustment oi the contact 42 along the resistance 40 as required to make the potential drop in the portion of that resistor at the right of the contact 42, as seen in Fig. 2. equal in magnitude and opposite in direction to the potential difference between the bridge terminals llc and 31d. The operation of the motor 44 adjusts the pen carriage 4I and thereby the contact 42 longitudinally of the motor shalt 44' as a result of a threaded connection between said pen carriage and shaft.

The thermal conductivity measuring means I1 and associated potentiometer instrument 3l need not be further described as each may be of a known form now in commercial use. For example, the thermal conductivity measuring means may be of the type disclosed in the Harrison Patent 1,818,619, granted August 11, 1931 fand the instrument 38 may be of the type disclosed in the patent application or Wills. Serial No. 421.173, filed December l, 1941.

As diagrammatically shown in Fig. 1. the Vdenection oi the pen carriage 43 effects a corresponding operation of each of the motors 29. 3u, Il. Il and 3l through a control system of known type and form. Said control system as diagrammatically illustrated, comprises a reversible electric motor 4I which is energized by the deflection Xoi' the pen carriage 43, for operation in a direction and to an extent determined by the direction and extent oi' said deflection. As shown by way of example in Figs. 2 and 3, the motor 45 is thus energized by virtue of its inclusion in an electric proportioning control system unit ot well known form. Said unit comprises a control contact 4B carried by the pen carriage 43 and adjusted by the dei'iection o! the latter along a slide wire resistor 41. The resistor 41 has its two terminals connected through coils 4l and 40, respectively to the terminals of a second slide wire resistor Il. The

resistor Il is engaged by` a follow-up contact li shown as in threaded engagement with the shaft oi the motor 4I so as to be adjusted along the resistor il by the rotation of the motor. The bridge circuit including the resistors 41 and Il and coils 48 and 4l, is energized by supply conductors $2 and $3, respectively connected to the contacts 4I and 5I. 'I'he motor 4l is energized from the supply conductors i! and Il for operation in one direction when a switch contact 54 is shifted out of its neutral position in one direction to engage a contact l5, or in the opposite direction into engagement with a second contact Il. The contacts $4 and l5 when in engagement close an energizing circuit for the motor causing the latter to operate in one direction. Similarly the contacts B4 and Il cooperate when in engagement to energize the motor 48 for rotation in the opposite direction.

I'he contact 54 is carried by the pivoted armature member B1 of an ,electromagnetic switch mechanism including the coils 4l and 49. When the control system. including the motor 4I is in its balanced condition. the contact I4 does not engage either of the contacts il and B8. When the system is unbalanced and the current flow through the coil 4l exceeds or is less than the current fiow through the coil 4l. the contact i4 is tilted into engagement with the contact 5i or Si. respectively. Said system is unbalanced by an adjustment o! the contact 4t along the resistor 41. The rotation of the motor 4l resulting from such unbalance is in the direction to rebalance the system by equalizing the current iiows through the coils 4I and 4l by its adjustment of the contact Bl along the resistor l0. The motor 45 continues to operate until the system is rebalanced and is then deenergized by the movement of the contact 54 into its neutral position.

The rotation o f the motor 45 which thus adjusts the contact ll as required to rebalance the controlling circuit for the motor, proportionately adjusts each oi' a plurality of control contacts 51 shown as in threaded engagement with the shaft of the motor 4l. Each of the contacts i1 engages a corresponding one of a series oi' slide wire resistors 5l, B9. I0. Il and B2, respectively included in the individual control circuits for the motors 29, 34. 3|, 3l and l5.

Each of said individual control circuits may be like the circuit shown in Fig. 3. and may be similarly associated with the motors 2l. l.. 3|, Il or 35 which it controls. As shown in Fig. 2. however. the individual control circuits for the last menticned motors include slide wire resistors $8', 59'. lo'. Bl' and Il', respectively connected in parallel with the resistors Il. 5|. B0, Il and 62. Each of said resistors IIL-82 is engaged by a manually adjustable contact ll and a manually adjustable switch I4 in association with each contact 4I and the corresponding contact 51 is adjustable to disconnect the corresponding bridg energizing conductor from the contact l1 and connect it to the associated contact il, so that the operation o! the corresponding motor may then be manually controlled.

As shown in Fig. 2. the shalt of the motor 4l carries an arm li which actuates a switch 8l tn ring an alarm bell I1 and light a signal lamp 4l on an abnormal upscale adjustment of the potentiometer control contact 46, such as might resuit from cooling water leakage into the hot lower Portion or the furnace as the result of a broken bosh plate .0r Mille.

In the contemplated normal use oi the apparatus shown in Figs. 1, 2 and 3, under any particular set of operating conditions. the various regulators 25, 2B, 28 and 34 and the indicator 32 are ilrst adjusted into their respective conditions assumed to be those insuring such approximation to the maximum efficiency of operation as is practically obtainable in steady operation under the prevailing operating conditions. Such calibrating adjustments of the regulators are readily effected by use of the manually adjustable contacts 63. With the apparatus thus properly calibrated, it should operate continuously without change in efficiency, so long as operating conditions do not change. In practice, however. the maintenance of the same general operating conditions do not prevent minor condition variations which impair the reduction capacity of the blast furnace and correspondingly vary the thermal conductivity of the exit furnace gas passing through the test cells 31a. When the exit gas thermal conductivity increases above or falls below the predetermined or assumed optimum value the resultant adjustment of the pen -carriage 43 moves the contact 46 along the resistor 41 and energizes the motor I5 to effect corrective adjustments tending to restore the normal thermal conductivity value.

As previously explained, when the thermal conductivity of the exit gas increases above the value assumed to be its optimum value. the corrective adjustments made should reduce the amount of hydrogen and carbon monoxide reducing agents in the furnace. Ordinarily the adjustments made to reduce the amount of hydrogen in the furnace comprise an adjustment of the regulator 34 directly reducing the rate at which hydrogen is passed into the furnace through the inlets I9, and an adjustment of the humidity regulator 25 which reduces the moisture content in the blast air and thus decreases the amount of hydrogen carried into the furnace in the form of water vapor. The adjustments ordinarily made to reduce the amount of carbon monoxide in the furnace comprise an adjustment of the regulator 26 to increase the volume .of the draft and an adjustment of the indicator 32' to indicate that the coke-ore ratio of the furnace charges should be reduced. A decrease in the moisture content of the blast air tends to temporarily increase the maximum furnace temperature. and the regulator 28 should ordinarily be adjusted to reduce the temperature of the blast air when its moisture content is reduced. It is to be noted, however. that while a change in the moisture content of the blast tends to an immediate change in the furnace hearth temperature. the hearth temperature produced results in a variation in the carbon monoxidecarbon dioxide ratio which will substantially eliminate hearth temperature change within a comparatively short operating period. even though no compensating adjustment in the blast temperature is made. Adjustments of the regulators 25, 26, 2B, 32' and 8| which are the converse of those just described. are made when the thermal conductivity of the test gas falls below the assumed optimum thermal conductivity.

On any change in general operating conditions. such as might result from a significant change in the character of the coke, iron ore. or fluxing agent charged into the furnace or in the rate of iron production. recalibration adjustments of the vregulators will ordinarily be necessary so that the furnace control system will tendtomaintain a new thermal conductivity value. assumed to be the optimum value for the changed operating conditions. The determination of the optimum thermal conductivity value for any new set of general operating conditions may well be g based in part on past experience. in part on the assumptions as to the effect of the changes made in the operating conditions and in part upon an estimate of the exit gas composition considered desirable under the new conditions. Thus. for example. it may be determined or assumed that with a given general set of operating conditions, the maximum emciency practically obtainable requires exit gas having the following composition by volume, namely, 12.5 parts of carbon dioxide, 25.4 parts of carbon monoxide, 3.5 parts of hydrogen and 58.6 parts of nitrogen and a small portion o1' other constituents which may be disregarded in this connection. The thermal conductivity of the exit gas constituents just enumerated are well known. On the assumption that Vat 32 F. the thermal conductivity of air is l, the thermal conductivity at the same temperature of carbon dioxide is .586; of carbon monoxide is .927: of hydrogen is 6.99; and of nitrogen is 1.003. 'I'he thermal conductivity of a mixture of the constituents just named depends of course upon the percentages of the diiTerent constituents in the mixture. On the exit gas composition assumptions just made, the thermal conductivity of the composition is approximately 1.12.

In Fig. 4 we have illustrated the use of our present invention in the control of a direct reduction furnace 'lil of the rabble furnace type comprising a vertical chamber within which are superposed stationary horizontal trays Il formed with ceni tral openings 'Il' Vand superposed stationary horizontal trays lllalternating with the trays 1i and formed with openings 12' at their peripheral edges. Associated with and above each of the trays 1|, are corresponding rabble arms 13 carried by a rotating shaft 14. Ore to be treated in the furnace is fed into the upper end of the furnace at a suitable rate by an ore feeder 15. In accordance with the present invention, carbon which may be in the form of coke, or which in some cases, may be in the form of coal, is passed into the upper end oi' the furnace chamber at a suitable rate in admixtiire with the ore fed by the ore feeder 15. or as in the construction diagrammatically illustrated, by a carbon feeder 1G separate from the ore feeder 15.

The bre and carbon charge thus fed into the furnace is moved slowly down over the trays 1I and 12 by the rabble arms 13, which work each ore body successively downward through the alternating tray openings 1I' and 12. Hydrogen containing gas is passed into the lower portion of the furnace chamber through openings 'l1 in its bottom wall and openings l1' in its side wall. In the furnace chamber, the furnace gases including hydrogen. continuously flow upward from the lower end of the chamber through the successive tray openings Il and 12', to a gas outlet 1B at the upper end oi' the furnace chamber.

The treated ore is moved out of the furnace at its lower end by gravitational action, supplemented by the action of sweeps 'I9 carried by the shaft 14, into a discharge chute lll leading to receiving apparatus El below the furnace. The latter may comprise means for separating gangue from the deoxiaed ore and for briquetting the latter to minimise its reoxidization and to better adapt it for treatment in a melting furnace. The

apparatus li may also include motor means for o,sos,ass

rotating the shaft 14. As the details of the apparatus 8i form no part of the present invention, they need not be illustrated in detail or further referred to herein.

The hydrogen containing gas passing into the furnace chamber through the openings 11 and II' is supplied through a manifold 82 which receives gas through a pipe I3 at a rate and in a condition regulated as hereinafter described. Ordinarily, the bulk of the gas passed to the furnace through the supply pipe 83, is gas which has passed out of the furnace through its gas outlet 'I8 and has thereafter passedthrough suitable conditioning apparatus. The conditioning apparatus illustrated diagrammatically by way of example in the accompanying drawings, comprises a heat exchanger l, a gas washer 0I to which gas is passed from the heat exchanger el by a booster pump ile, and a precipitator 81. The latter receives washed gas from the gas washer B5 through a conduit 88 and discharges the gas into a distribution pipe t9. The cooling and cleaning actions to which the gas is subjected in passing through the heat exchanger Il, gas washer B5 and precipitator 0l, eliminate some of the carbon dioxide. much of the water vapor and practically all of the dust contained in the gas as it passes away from the furnace.

As shown, gas may pass from the distribution pipe 8l to a gas holder 80 and to the inlets of booster pumps 0l and 92. The pump 92 may supply gas through its outletpipe 93 to any apparatus in which the gas may be used advantageously. The pump 9| supplies gas at a rate regulated as hereinafter described to the inlet pipe 94 of a humidity regulator 0l. The latter may also receive hydrogen containing gas from a make-up gas supply pipe 90. The gas passing through the humidity regulator l! is delivered to the inlet $1 of the heat exchanger 0I, and passes away from the latter through the heat exchanger outlet 9B to a gas heater orpreheater 99 from which the gas to the furnace supply pipe 03. The gas thus passing through the heat exchanger between its inlet 01 and outlet 9B absorbs heat from the furnace exit gas drawn `through the heat exchanger by the pump 8B.

The gas thus passing through the preheater 99 absorbs heat from hot products of combustion of fluid fuel burning in a furnace chamber iiiii; said fuel, which may be gas supplied at a regulated rate by thepipe ll, is passed into the chamber |00 through a pipe IM. Products of combustion pass from the chamber |00 to thegas heater 98 through a pipe |02. and pass away from the heater 98 through a stack connection |03.

In the contemplated operation of the apparatus shown in the drawings, ore and carbon are fed into the furnace l0 by the feeders 'i6 and ll, respectively, at suitable rates. As diagrammatically shown in the drawings. the feed rates of the feeders Il and I6 may be simultaneously and proportionally adjusted through regulators |05 and |08. respectively. by the angular adjustment of a manually rotatable control element |01. The ratio of the carbon and ore feed rates which the regulating elements |05, |08 and w1 tend to maintain, can be varied by means of a control element |08 which by its adjustment varies the rate at which carbon is fed by the feeder I6 in any particular adjustment of its regulator |08.

The rate at which hydrogen containing gas is passed into the furnace through the manifold Il, is directly regulated by a nuid pressure motor valve Ill in the outlet pipe of the blower DI. As

showmthevalve iilisadjustedtovarythegas now from the blower Il to the humidity regulator 05. by a iiow meter ilii responsive to the pressure drop of the gas flowing through a measuring orice Iii in the pipe 94. The flow meter lil adjusts the valve |09 as required to maintain at the orifice Iii a pressure drop determined by a Vcontrol yelement Il! which may be adjusted to vary said pressure drop and thereby the rate of gas now through the pipe 94. The rate at which make-up gas is passed into the pipe B4 by the pipe 9B. is regulated by a fluid pressure motor valve lit which is controlled by a flow meter IM re sponsive to the pressure drop at a measuring orifice H5 in the pipe 08. The now meter iM adjusts the valve H3 as required to maintain a pressure drop at and flow through the orifice III which is determined by the adjustment of a control element H6.

The humidity controller is adapted to operate to increase or decrease the moisture content of the gas passing through it as required to maintain that content at a value determined by a control element il'l which may be adjusted to vary said content. The temperature at which the gas passes away from the heater 99 is controlled by the adjustment of a uid pressure motor valve i l0 in the fuel supply pipe lili for the combustion chamber i00. The valve IIB is automatically adjusted by a control pyrometer I i0 responsive to a suitable controlling temperature which may be the temperature in the combustion chamber |00 or, as shown, the temperature of a thermocouple i2i in the outlet 83 of the gas preheater 08. The control pyrometer IIB tends to maintain a gas temperature which is predetermined and may be varied by adjustment of a. control ement |20.

In the normal. intended operation of the furnace shown in Fig. 4, iron ore, ordinarily hematite (FeaOs), or magnetite (FeaOi), and carbon are fed into the upper end of the furnace chamber and hydrogen containing gas is passed into the lower end of the furnace chamber at suitably related rates. As shown the rates at which ore and carbon are supplied to the furnace may be varied by adjustment of the regulating device |01, and the rate at which carbon is supplied may be independently regulated by the control element itil. The rate at which hydrogen containing gas is passed into the furnace is subject to regulation by the control element H2. The gas supplied to the furnace through the inlets il and l1 may well be preheated to a temperature of about 800 C. As a result of such preheating and the exothermic reducing actions effected in the furnace chamber. a temperature of about 800 C. is maintained in the lower end of the furnace chamber. Those reducing actions convert large portions, at least, of the iron oxide ores into metallic iron. The reduction is effected partly by carbon monoxide, but. mainly by hydrogen with a resultant formation of water vapor. The latter is continuoushr being decomposed in the furnace by reaction with carbon. with a resultant formation of free hydrogen (H2) and carbon monoxide (CO) and/or carbon dioxide (CO2) The exit gas leaving the furnace chamber through the outlet 18 includes free hydrogen. water vapor, carbon monoxide, and carbon dioxide. A suitable relation between the rates at which ore and carbon are supplied to the upper end of the furnace and the rate at which reducing gas is supplied to the lower end of the furnace, and the inclusion of a. suitable freehydrogen content in said reducing gas are necessarytothemaintensnceofthe desired operating conditions. With the particular arrangement shownthoseconditionsmayberegulatedbysuitable adjustments of the control elements in, II! and III. They could be maintained without use of the element II'I if the humidity regulator Il were omitted and the gas washer II were operated to maintain a substantially constant moisture Vcontent in the gas leaving it. Advantageously, the rate at which make-up gas is supplied through the pipe It, and the temperature at which the hydrogen containing sas is supplied to the furnace are subiect to adiustment of the control elements lil and III. respectively.

In the form of our invention illustrated in Fig. s, each of theicontrol elements lill, lil. IIS, II'I and Ill is a reversible electric motor, and each of said motors is controlled by measuring apparatus il! through a control instrument |23 and control apparatus |24 which may be respectively identical with the measuring apparatus l1, control instrument Sl and control apparatus Il of Pigs.1 and2. AsshowninFlg.4.asample stream of gas is passed continuously to the measuring apparatus Ill from the furnace outlet 1li, through a pipe III and a suitable gas conditioning apparatus III like or analogous to the conditioner of Fig. 1.

For operation at maximum practicalyeiiiciency under any given set of general operating conditions, the thermal conductivity of the exit gas measured by the measuring apparatus |22 will have a certain assumed optimum value which can bedeterminedempiricaliy,orasaresultofpast experience, observations andl assumptions based on the furnace operating conditions. However. the assumed optimum thermal conductivity value be determined, the control apparatus Ill is adapted to maintain or tends to maintain, that value by actuating the motors Ilf, iII and lill to decrease and increase the rates at which hydrogen and carbon are supplied to the furnace as the thermal conductivity of the exit gases increases and decreases respectively, and by operating the motor III to increase and decrease the temperature of the hydrogen containing gas supplied to the furnace as the moisture content of that gasis decreased and increased. As those skilled in the art will recognize. general advantages of the present invention are obtainable without the use of all of the various control elements shownin Fis. l and inria- 4 as automatically` controlled reversible motors. Y

`Theintroductionofcarbonintothefurnacel provided for in Hg. 4. forms no part of our ioint invention butisdisclcsed and oiaimedinthecopendinl lolo application, Serial No. 610,125, med

of even date herewith by John R. Green. `one of the Joint applicants herein. It u-to be noted, moreover. that the omissionV or non-use of the cokefeeder'llshowninliig.4willnctinterfere withtheattainmentof the generaladvantages of furnace of Fil. l will not interfere with the at-V tainmantofthegeneraiadvantagesofthepresthepreaentinventionwhenusedtocontroltl'ie .operationofth ent invention when used to control the operation of a conventional blast furnace.

As previously pointed out. the thermal conductivity of the exit gas is not the only property or characteristic of that gas which can be readily measured continuously, and the measure of which forms a measure of thel reduction capacity of the furnace which can be utilized in adjusting the furnace to approximate the maximum practical eiilciency. As will be apparent from a consideration of their molecular weights. the density of carbon dioxide is appreciably greater and the density of hydrogen is appreciably smaller than thedensity of other gaseous constituents present in significant amounts in the exit gases of the furnaces shown in Figs. l and 4. In consequence. when either of the furnaces shown in Figs. l and 4 is controlled in accordance with the present invention, the hydrogen and carbon monoxide contents of the furnace gases should be increased on an increase in the exit gas density, and should be reduced ona decrease in the density of the exit gas. Various meters for measuring the density Yof gases are available for use in such a control system as is shown in Fig. 2, in lieu of the potentiometers 38 and 3l shown in the drawings: One such meter, Ill, adapted for auch use and shown diagrammatically in Fig. 5, comprises an arm III which deects to the right or left as the density of the furnace gas increases and decreases. The arm carries a contact ill, and as the arm Ill deiiects in accordance with variations in furnace gas density, it adjusts the contact I!! along a slide wire resistor I'I which may be included in a control system exactly like that shown in Figs. 2 and 3.

A's previously indicated, the name structure of a burning 'iet of gas consisting wholly or in substantial `part of exit gas from a reducing furnace varies with the reducing character of the furnace atmosphere in such manner as to provide a measurable indication of said capacity which may be used in controlling the operation of the furnace. Thus, as diagrammatically illustrated in Fig. 6, furnace exit gas which may have passed through the conditioning element II of Fig. 1 or I 2i of Fig. 4, may be passed through a pipe lll to a burner III at a rate controlled by the adjustment of a regulating valve |32. As shown in Fig. 6, the furnace exit gas supplied to the pipe IIII may or may not be mixed with a gas of higher B. t. u. value such as methane, propane or butane, supplied through a pipe III. Amixing valve III is provided to regulate the relative amounts of gas supplied by the pipes ill and III in the mixture passed to the burner III. The mixture of .high B. t. u. gas with the furnace exit gas insures the maintenance of a stronger burner flame than the combustion of the unmixed furnace exit gas will give. When the addition of the high B. t. u. gas is not required, a cutoB-valve i in the pipe Il! may be closed. In lieu oi mixing ahigh B. t. u. gas with the furnace exit gas thelatter may be burned in the presence of iess'combustion air than is required for complete combustion.

The burned -gas discharged by the burner III forms a flame comprising a body or outer cone portion l and an inner cone portion |31 enveloped by the portion Ill. The form.Y and particularly thel length of the flame inner cone |31 changes as a result of changes in the composition of the gas which gives rise to differences-in the rate of flame propagation. In particular, an increase or decrease in the hydrogen-carbon dioxide Hs/CO: ratio will respectively elongate or assaut shorten the inner flame cone |31. The length of that cone, and particularly the relative lengths of the cones |31 and |39 th provide a reliable indication ot the reducing c ter of the furnace atmosphere.

As shown in Fig. 6, the variations in the relative form of the flame portion |39 and |31 are utilized in a known manner to indicate variations in the composition of the gas supplied to the burner. To this end thermocouples |39 have their hot junctions inserted in the outer envelope portion |39 of the flame at suitably distributed points. As shown. there are four thermocouples |38 and two of them h'ave their hot Junctions symmetrically located at opposite sides of the flame axis and at a level which is below the tip of the inner ame cone |31 when the latter is of normal length. The other two thermocouples |39 have their hot junctions symmetrically disposed at opposite sides of the flame axis at a level which is well above the upper end of the inner flame cone |31 when the latter is of normal length. i

The four thermocouples |99 are connected in series with one another and with a suitable potential measuring instrument |39. As shown, the thermocouples are thus connected. in series with such references to their respective polarities that the two thermocouples of each pair at the same level act additively on the instrument |39, while the thcrmocouples at the different levels act differentially on the instrument |39. As shown, the instrument |39 comprises an arm |40 which may be arranged to deflect clockwise or counter-clockwise as a result of an increase or decrease, respec tively, in the hydrogen-carbon dioxide ratio of the gas supplied to the burner ISI.

As diagrammatically shown in Fig. 6, the arm lili carries a contact lli engaging and moving along a slide wire I1. The contact Ill and resistor l1 of Fig. 6 are adapted to coact as do contact 49 and resistor 91 of Fig. 2 in a control system like that shown in Fig. 2 and in such case, the contact lll and associated resistor 41 are adapted to control the associated furnace in automatic response to the reducing character of the furnace atmosphere as indicated by the flame propagation rate of the furnace exit gas, in the same general manner as the furnace is controlled with the arrangements shown in Figs. 1 and 4 in accordance with variations in the reducing character of the furnace atmosphere indicated by the thermal conductivity of the furnace exit gas.

The means shown diagrammatically in Fig. 6 for analyzing the structure of the burner name formation is no part of the present invention, but is fully disclosed and claimed in the prior Krogh Patent 2,052,181, granted August 25, 1936, and therefore need not be further illustrated or described herein.

While in accordance with the provisions of the statutes, we have illustrated and described the best forms of embodiment of our invention now known to us, it will be apparent to those skilled in the art that changes may be made in the forms and use of the apparatus disclosed herein. without departing from the spirit of ou: invention as set forth in the appended claims, and that in some cases certain features of our invention may be used to advantage without a corresponding use of other features.

Having now described our invention. what we claim as new and desire to secure by Letters Patent is:

1. In reducing metallic oxide ore in a blast mrnace in which pre-heated air is used as a blast and in which a furnace gas atmosphere including reducing and non-reducing gases is maintained. the method which consists in determining the reducing capacity of the exit gases and vpassing gaseous material into the furnace at a point above the mantle to correctively modify this reducing capacity in one direction or another in accordance with said determination.

l0 2. In reducing metallic oxide ore in a blast furnace in which pre-heated air is used as a blast and in which the furnace gas atmosphere includes a reducing portion consisting of lwdrogen and carbon monoxide and a non-reducing portion including carbon dioxide in amount varying in. versely with the amount of carbon monoxide in said reducing portion, the method which consists in determining the reducing capacity of the furnace exit gases which reducing capacity varies in value in one direction or the other as a result of an increase'or decrease, respectively, in its` hyy drogen content, and as a result of a decrease or increase, respectively in its carbon dioxide content and passing gaseous material into thc iurnace at a. point above` the mantle to increase or decrease the reducing portion of said exit gases as this reducing capacity varies from a predetermined value thereof in one direction or the other, respectively.

3. In reducing metallic oxide ore in a blast furnace in which pre-heated air i: used as a blast and in which a gaseous atmosphere including a reducing portion consisting of hydrogen and carbon monoxide is maintained and from which gas is continuously withdrawn, the method which consists in determining the reducing capacity ot the gas withdrawn which is varied in one direction by an increase in its hydrogen content and by an increase in its carbon monoxide content and is varied in the opposite direction and by a decrease in its hydrogen content and by a decrease in its carbon monoxide content, and pass ing gaseous material into the furnace at a point above the mantle to increase or decrease the re- 45 ducing portion of the gas withdrawn accordingly as this reducing capacity varies in one direction or the other, respectively from a predetermined amount.

4. The combination with a metallic oxide ore 50 reducing furnace, of means for feeding ore, carbon and hydrogen into the furnace, regulating mechanism adjustable to regulate the reducing capacity of the gas in the furnace and control mechanism including measuring means for meas- 55 uring a measurable property of said gas which is indicative of the reducing capacity of the gas and also including means for adjusting said regulating mechanism in response to variations in the meas# urements of said measurable property.

5. The combination with a metallic oxide ore reducing furnace having a furnace chamber with a gas outlet, means for feeding ore, carbon and hydrogen into the furnace chamber, regulating mechanism adjustable to regulate the aggregate hydrogen and Icarbon monoxide constituents of the gas in the furnace chamber and control mechanism including measuring means for measuring a measurable property of the gas leaving the furnace chamber through said outlet and varying in 7 accordance with variations in the aggregate hydrogen and carbon monoxide constituents of said gas and also including means for adjusting said regulating mechanism in response to variations in the measurements of said measurable property. 1s c. The combination with a metallic oxide orc reducing furnace of means for supplyins solid material including metallic oxide ore and coke to the furnace. means for supplying gaseous material including hydrogen to the furnace, means for preheating gaseous material supplied to the furnace. means for varying the moisture content of the gaseous material supplied to the furnace, and control mechanism including means for measuring a measurable property of the furnace gas which is indicative of the reducing capacity of the furnace atmosphere and also including means for regulating the rates at which carbon and hydrogenl are supplied to the furnace and the amounts of moisture and heat in the gaseous material supplied to the furnace in accordance with variations in said reducing capacity.

7. The combination with a metallic oxide ore reducing furnace means for supplying solid material including metallic oxide ore and coke to the the furnace. means for supplying gaseous material including hydrogen to the furnace, means for preheating gaseous material supplied to the furnace, means for varying the moisture content of the gaseous material supplied to the furnace, and control mechanism including measuring means for measuring a measurable property of the gas which is indicative of the aggregate reducing capacity of the hydrogen and carbon monoxide in the furnace atmosphere and also including regulating means controlled by said measuring means for regulating the rates at which carbon and hydrogen are supplied to the furnace and the amounts of moisture and heat in the gaseous material supplied to the furnace in accordance with variations in said reducing capacity from a normal value thereof.

8. In the method of operating a blast furnace which comprises charging into the furnace materials including oxide ore and carbon and introducing a reducing gas into the furnace at a point above the mantle thereof and blowing air through the charge to cause reduction of the ore and to maintain an atmosphere including reducing and non-reducing gases, the steps of controlling the operation of said furnace comprising determining the reducing capacity of the exit gases and correctively modifying this reducing capacity in one direction or the other in accordance with said determination by regulating the introduction oi said reducing gas into the furnace.

JOHN R. GREEN. JOSEPH P. VOLLRATH.

Certificate of Correction Patent No. 2,395,385.

February 19, 1946.

JOHN R. GREEN ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 37,

for ement read element; (im read Serial No. 510,126; an t e 6, first column, line 57, lfor Serial No. .510,125 at the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Signed and sealed nthis 30th day of April, A. D. 1946.

[aan] LESLIE FRAZEB,

First Assistant Commissioner of Patents.

reducing furnace of means for supplyins solid material including metallic oxide ore and coke to the furnace. means for supplying gaseous material including hydrogen to the furnace, means for preheating gaseous material supplied to the furnace. means for varying the moisture content of the gaseous material supplied to the furnace, and control mechanism including means for measuring a measurable property of the furnace gas which is indicative of the reducing capacity of the furnace atmosphere and also including means for regulating the rates at which carbon and hydrogenl are supplied to the furnace and the amounts of moisture and heat in the gaseous material supplied to the furnace in accordance with variations in said reducing capacity.

7. The combination with a metallic oxide ore reducing furnace means for supplying solid material including metallic oxide ore and coke to the the furnace. means for supplying gaseous material including hydrogen to the furnace, means for preheating gaseous material supplied to the furnace, means for varying the moisture content of the gaseous material supplied to the furnace, and control mechanism including measuring means for measuring a measurable property of the gas which is indicative of the aggregate reducing capacity of the hydrogen and carbon monoxide in the furnace atmosphere and also including regulating means controlled by said measuring means for regulating the rates at which carbon and hydrogen are supplied to the furnace and the amounts of moisture and heat in the gaseous material supplied to the furnace in accordance with variations in said reducing capacity from a normal value thereof.

8. In the method of operating a blast furnace which comprises charging into the furnace materials including oxide ore and carbon and introducing a reducing gas into the furnace at a point above the mantle thereof and blowing air through the charge to cause reduction of the ore and to maintain an atmosphere including reducing and non-reducing gases, the steps of controlling the operation of said furnace comprising determining the reducing capacity of the exit gases and correctively modifying this reducing capacity in one direction or the other in accordance with said determination by regulating the introduction oi said reducing gas into the furnace.

JOHN R. GREEN. JOSEPH P. VOLLRATH.

Certificate of Correction Patent No. 2,395,385.

February 19, 1946.

JOHN R. GREEN ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 37,

for ement read element; (im read Serial No. 510,126; an t e 6, first column, line 57, lfor Serial No. .510,125 at the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Signed and sealed nthis 30th day of April, A. D. 1946.

[aan] LESLIE FRAZEB,

First Assistant Commissioner of Patents. 

